Cells

Question 1

eukaryotic cells

Answer 1

animal, plant cells. alage and fungi cells

Question 2

specialised cells

Answer 2

Multicellular eukaryotic organism- cells become specialised (specific function)
cell structure helps carry out its function
specialised cells>tissue>organs>organ system

Question 3

Viruses are acellular. not cells

Answer 3

• viruses are nucleic acid surrounded by protein, not alive
• no plasma membrane, no cytoplasm, no ribosomes
• all viruses invade and reproduce inside the cells of another organism (host cell)
• viruses contain a core of genetic material, either dna or rna
• protein coat around the core is a capsid
• attachment proteins stick out from the - - edge of the capsid, these let a virus cling onto a host cell

Question 4

prokaryotic cells replicate by binary fission

Answer 4

in binary fission, the cell replicates of its genetic material
- 1, circular dna and plasmids replicate, the main dna loop is only replicated once, but plasmids can be replicated many times.
- 2, the cell gets bigger and the dna moves to opposite poles of the cell
- 3, cytoplasm begin to devide, new cell wall begins to form
- 4, cytoplasm divides, two daughter cells are produces, each daughter cell has a copy of the circular dna, but can have a varied number of plasmids

Question 5

Virus replication

Answer 5

• use attachment proteins to bind to a complementary receptor protein on the surface of host cells.
• different viruses have different attachment proteins and so a different receptor protein is needed on the host cell-> some viruses can only infect certain cells, some can infect many
• viruses arent alive so they dont undergo cell division, they instead inject their dna or rna into the host cell, which uses it enzymes or ribosomes to replicate the virus

Question 6

Magnification= image size/actual size

Answer 6

Magnification- the size, how much bigger the image is compared to the specimen/sample

Resolution- how detailed the image is, how well a microscope distinguishes between two points that are close together

Question 7

Optical microscopes (light microscopes)

Answer 7

-use light to form an image
- max resolution of 0.2 micrometers (can’t view ribosomes, endoplasmic reticulum, lysosomes) may be able to see nucleus and mitochondria
- max mag is x1500

Question 8

Electron microscopes

Answer 8

• use electrons to form an image
• higher resolution than optical, can look at more organelles
• max resolution of 0.0002 micrometers (1000x higher than optical)
• max mag is about 1,500,000x
• can be scanning or transmission

Question 9

Electron microscopes, Transmission, electron microscopes (TEMs)

Answer 9

• use electromagnets to focus beams of electrons which are then transmitted through the specimen
• denser parts absorb more electrons, which make them look darker on the final image
• good bc they give high res images, you can see the internal structure of the organelles eg chloroplast
• can only be used on thin specimens

Question 10

Electron microscopes, Scanning Electron Microscopes (SEMs)

Answer 10

• SEMs scan a beam of electrons across the specimen. This knocks off electrons from the specimen, which are then gathered in a cathode ray tube to form an image
• this image shows the surface of the specimen, and can be 3D
• SEMs are good because they can be used on thick specimens
• they give lower resolution images than TEMs

Question 11

you can view specimens under an optical microscope using slides

Answer 11

• ‘temporary mount’ of specimen on slide
• pippet a small drop of water on the slide, use tweezers to place a thin section of specimen on top of the waterdrop
• add a drop of stain, which highlights objects in the cell. eg eosin is used to make cytoplasm show up. Iodine in potassium iodine solution stains starch grains of plant cells
• add the cover slip to protect the specimen. be careful of air bubbles

Question 12

Cell fractionation, Homogenisation/breaking up the cell (step one)

Answer 12

• can be done by vibrating or grinding up the cells in a blender to break up the plasma membrane and release the organelles into the solution
• must be in an ice cold solution to reduce the activity of enzymes that break down organelles
• must be an isotonic solution, meaning it has the same concentration of chemicals as the cells being broken down in order to prevent damage to the organelles through osmosis
• ## a buffer solution should be added to maintain the pH

Question 13

Cell fractionation, filtration (step two)

Answer 13

• the homogenised solution is filtered through a gauze to separate any large cell debris or tissue debris, eg connective tissue from the organelle
• organelles are smaller than debris so they pass through the gauze

Question 14

Cell fractionation, separating the organelles (step 3)

Answer 14

After filtering, you’re left w a solution w a mixture of organelles- separating one from another needs ultracentrifugation
- poured into a tub then put into a centrifuge, which separates material by spinning. Spin at a low speed so the heavier organelles like nuclei got flung to the bottom. this forms a thick sediment at the bottom (the pellet) the rest are in the fluid above the sediment (supernatant)

• supernatant is drained off and poured into another tube, then spun at a higher speed, heaviest organelle (mitochondria) from a pellet at the bottom. supernatant is drained off and spun at a higher speed
• repeated at higher and higher speeds until all of the organelles have been separated. each time the pellet is made of lighter organelles.

Question 15

Mitosis, produces genetically identical cells

Answer 15

• mitosis: parent cell divides to produce two genetically identical daughter cells
• Mitosis is needed for the growth of multicellular organism and for repairing damaged tissue
• cells that are able to keep their ability to divide follow a cell cycle, mitosis is part of the cycle.

Question 16

What are the four stages of mitosis?

Answer 16

Interphase
Prophase
Metaphase
Anaphase
Telophase

Question 17

What is Anaphase?

Answer 17

The centromeres divide, seperating each pair of sister chromatids.
The spindles contract, pulling chromatids to opposite poles of the spindle, centromere first. This makes chromatids appear v-shaped

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what is telophase? - The chromatids reach the opposite poles on the spindle, they uncoil to be long and thin again, they are now chromosomes again.
- a nuclear envolope forms around each group of chromosomes, now there are two nuclei
- division of the cytoplasm, (aka, cytokinesis~anaphase) finishes in telophase
- there are now two genetically identical daughter cells. mitosis is finished and the daughter cells start interpahse ready for another mitosis.

new card. how do you calculate mitosis?
observed that 10/100 cells are in metaphase, suggests that metaphase must be 10/100th of a cell cycle. told a cell cycle last 15 hours, convert into mins, then times by the division.

new card
what is the cause of cancer?
- uncontrolled cell divison.
- mitosis and the cell cycle are controlled by genes
- normally when cells have divided enough times to make enough new cells, they stop but if theres a mutation in the gene that control cells division, it grows out of control
- the cells keep on dividing to make more cells, which form a tumour
- cancer is a tumour that invades surrounding tissue

new card

Some cancer treatment targets the cell cycle
- some treatments for cancer are designed to control the rate of cell division in tumour cells by disrupting the cell cycle which kills tumour cells but cant distinguish from a normal cell so kills dividing body cells
- tumour cells divide more frequently so the treatment is more likely to kill them

new card
what do cell cycles do cancer treatments target?

• G1, cell growth and protein production, chemical drugs like chemotherapy preent

Question 17

What is Interphase?

Answer 17

The cell carries out normal functions, preprases to divide
- the cells dna is unravalled and replicated to double its genetic content
- the organelles are also replicated
- ATP content is increased to provide energy for cell division

Question 18

What is prophase?

Answer 18

• chromosomes condense, get shorter and fatter
• centrioles (tiny bundles of protien) start moving to the opposite end of the cell. This forms a network of protien fibres across it called the spindle
• The nuclear envelope (membrane around the nucleus) breaks down and chromosomes lie free in the cytoplasm

Question 19

What is the metaphase?

Answer 19

Chromosomes, each w two chromatids, line up along the middle of the cell and become fully attached to the spindle by their centromere

Question 20

Cell cycle

Answer 20

consists of a period of cell growth and dna replication which is interphase, mitosis happens after that. Interphase is divided into three separate growth stages. G1, S, and G2

Question 22

Cell membranes control what passes through them

Question 23

Exchange across cell membranes, active transport needs energy

Answer 23

active transport uses energy to move molecules and ions across membranes
It involves carrier proteins, sim to facilitated diffusion, a molecule attaches to the carrier protein, the protein changes shape and this moved the molecule across the membrane and releases it on the other side

2 main differences:
- active transport usually moves the solute from a low to high conc, but fac dif is a high to low
- act tr requires energy, fac dif does not. ATP- common source of energy in the cell, produced by resp, ATP undergoes a hydrolysis reaction, which splits into ADP and Pi (inorg phosphate) which releases energy so the solute can be transported

Question 24

Co transporters are a type of carrier protein

Answer 24

• they bind 2 molecules at a time
• the conc grad of one of the molecules is used to move the other molecule against is own conc grad
• like sodium ions and glucose

Question 25

What are factors that affecting the rate of active transport

Answer 25

• speed of the individual carrier proteins, the faster they work, the faster the rate of act tr
• number of carrier proteins present, more proteins, faster rate of active transport
• rate of resp in the cell, availability of ATP. if resp is inhibited active transport cant take place

Question 26

Why is glucose involved in co-transport?

Answer 26

• glucose is absorbed into the bloodstream in the small intestine.
• in the ileum (the final part of the small intestine) the conc of glucose is too low for it to diffuse out of the blood. so its absorbed from the lumen (middle) of the ileum by co transport

Question 27

What happens during co-transport in the mammalian lleum?

Answer 27

• Glucose enters the ileum epithelium with sodium ions, which are actively transported out of the ileum epithelial cells into the blood, by the sodium-potassium pump, this creates a conc grad. there’s now a higher conc of sodium ions in the lumen of the ileum than inside the cell
• this causes sodium ions to diffuse from the lumen of the ileum into the epithelial cell and down the conc grad, they do this through the sodium-glucose co-transporter proteins.
• the co transporter carries glucose into the cell with the sodium as a result, the conc of glucose inside the cell increases
• glucose diffuses out of the cell, into the blood, down its conc grad through a protein channel by facilitated diffusion

Question 28

Foreign antigen trigger an immune response

Answer 28

• Antigens (molecules that are usually proteins) generate an immune response when theyre detected by the body.
• Usually on the surface of cells and used by the immune system to identify pathogens, abnormal body cells, toxins and cells from other individuals of the same species (organ trans)

Question 29

What are the four main stages of the immune response

Answer 29

1) phagocytes engulf pathogens
2) phagocytes activate T-cells
3) T-cells activate B-cells, which divide into plasma cells
4) plasma cells make more antibodies to a specific antigen

Question 30

Immune response #1: phagocytosis

Answer 30

A phagocyte is a type of wbc found in the blood, and tissue. Its the first cells to respond to an immune trigger inside the body
- phagocyte recognises the foreign antigen on a pathogen
- cytoplasm of the phagocyte moved round the pathogen, engulfing it
- pathogen is contained inside a phagocytic vacuole/bubble in the cytoplasm
- a lysosome (organelles containing lysozyme enzymes) fuse w the phagocytic vacuole. the lysozymes break down the pathogen
- Phagocytes then present the pathogens antigens, it sticks the antigens on it surface to activate other immune system cells

Question 31

immune response #2: phagocytes activate t cells

Answer 31

T-cells/T lymphocytes are a type of wbc with receptor proteins on its surface they bind to complementary antigens presented by phagocytes which activates the T-cell
- helper T-cells release chemical signals that activate and stimulate phagocytes and cytotoxic T-cells
- cytotoxic T cells kill abnormal and foreign cells
- T helper cells activate B cells, which secrete antibodies

Question 32

immune response #3 T cells activate B-cells which divide into plasma cells

Answer 32

• B-cells/b lymphocytes are a type of wbc that are covered in antibodies (proteins that bind antigens to form an antigen-antibody complex) each b cell is shaped differently, so each one binds to differently shaped antigens
• when the antibody on the surface of a b cell meets a complementary shaped antigen, it binds to it
• this, along w the substances released from the helper t cells, activate the b cells (aka clonal selection)
• This activates B cells to divide into plasma cells

Question 33

Immune response #4: plasma cells make more antibodies to specific antigens

Answer 33

plasma cells are clones of B cells so they’re identical. they secrete lots of antibodies specific to the antigen (monoclonal antibodies) these bind to the antigens on the surface of the pathogen to form lots of antigen-antibody complexes
An antibody has two binding sites, so can bind to two pathogens at once (called agglutination) phagocytes then bind to the antibodies and phagocytose many pathogens at once. this process leads to destruction of the pathogen carrying the anitgen in the body

Question 34

What are cellular and humoral immune responses?

Answer 34

Cellular- T cells and other immune system cells they interact w. eg phagocytes

humoral- B cells, clonal selection and the production of mcab

Question 35

What is the primary immune repsonse?

Answer 35

• if an antigen enters the body for the first time it activates the immune system (primary response)
• This is slow bc there arent many b cells that can make the antibody needed to bind to it
• eventually the body will produce enough of the right antibody to overcome the infection (person will show symptoms)
• after being exposed to an antigen t and b cells produce memory cells which remain in the body for a long time. memory t cells remember the specific antigen and will recognise it if it comes back. memory b cells record the specific antibodies needed to bind the antigen
• immunity achieved, can respond quickly to a second infection

Question 36

What is the secondary immune response?

Answer 36

• if the same pathogen comes back the immune response will produce a quicker, stronger immune response (sec resp)
• clonal selection happens faster. memory b cells are activated and divide into plasma cells that produce the right antibody to the antigen.
• Memory T cells are activated and divide into the correct type of T cell to kill the cell carrying the antigen
• secondary response gets rid of pathogens before symptoms (immunity)

Question 42

Centrifuge rules ! (?)

Answer 42

First the cells are blended in a homogeniser (forms homogenise fluid)
Put in centrifuge and spun at a slow speed
Heaviest organelles are forced to the bottom where a sediment forms.
Supernatant (fluid at the top) is removed

Heaviest ➡️lightest

Nuclei
Chloroplast if plant
Mitochondria
Lysosomes
Endoplasmic reticulum
Ribosomes

Question 43

Centrifuge rules ! (?)

Answer 43

First the cells are blended in a homogeniser (forms homogenise fluid)
Put in centrifuge and spun at a slow speed
Heaviest organelles are forced to the bottom where a sediment forms.
Supernatant (fluid at the top) is removed

Heaviest ➡️lightest

Nuclei
Chloroplast if plant
Mitochondria
Lysosomes
Endoplasmic reticulum
Ribosomes